Vehicle braking system with active hydraulic brake force assistance and control method for the same

ABSTRACT

In a method of controlling a hydraulic vehicle brake system with active hydraulic brake force boosting, wherein the driver can introduce brake pressure into a master brake cylinder with an actuating device, wherein the pressure introduced by the driver is boosted by an active hydraulic pressure increasing unit, a braking request or a suspected braking request of the driver is determined and, when a braking request or a suspected braking request of the driver is detected, a separating valve that is arranged in a line connecting the master brake cylinder and the hydraulic pressure increasing unit is opened or remains open and the pressure increasing unit is actuated for pressure generation purposes.

TECHNICAL FIELD

The present invention relates to a method of controlling a hydraulicvehicle brake system with an active hydraulic brake force boosting,wherein the driver can introduce brake pressure into a master brakecylinder by means of an actuating device, preferably a brake pedal, andwherein the pressure introduced by the driver is boosted by means of anactive hydraulic pressure increasing unit, in particular a hydraulicpump.

The invention likewise relates to a hydraulic brake system for vehiclesincluding a master brake cylinder operable by means of an actuatingdevice, preferably a brake pedal, and including at least one pump, thepressure of which can be applied to at least one wheel brake of thevehicle for the purpose of producing hydraulic brake force boosting,which pump is adapted to be connected on the inlet side (suction side)to the master brake cylinder by way of at least one hydraulic conduitinto which a change-over valve is inserted, while the pump is adapted tobe connected on the outlet side (pressure side) to at least one wheelbrake of the vehicle by way of at least one hydraulic conduit and to themaster brake cylinder by way of at least one hydraulic conduit intowhich a separating valve is inserted.

BACKGROUND OF THE INVENTION

Vacuum brake boosters require a vacuum supply from the engine in orderto assist the pedal force to be generated by the driver. Currently, asufficient vacuum supply for brake force assistance becomes more rare atan increasing rate in new engine technology such as gasoline directinjection engines or Diesel engines. Additional auxiliary energy becomesnecessary to assist the driver in braking. In determined systems, thedriver's force is converted into hydraulic pressure by means of a vacuumbrake booster and a tandem master brake cylinder (TMC), said hydraulicpressure being measured by pressure sensors at the outlet of the tandemmaster brake cylinder. One possibility of the additional brake forceassistance is realized in brake systems with active hydraulic brakeforce assistance in that additional hydraulic pressure is produced bymeans of a pressure increasing unit.

Due to inertias and clearances in the system and due to the limitedcapacity of the pump, it is problematic in this pressure development toachieve a uniform pressure buildup with a desired characteristic curve.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to improve and further develop a methodand a brake system of the type referred to hereinabove in such a fashionthat its shortcomings are avoided. The objective is in particular todesign the brake system and the method in such a fashion that the brakepressure buildup is improved at the beginning of a braking operation.

This object is achieved by the features of the independent patentclaims.

In a method of the above-mentioned type, the invention according toclaim 1 arranges that a braking request or a suspected braking requestof the driver is determined and, when a braking request or a suspectedbraking request of the driver is detected, a separating valve that isarranged in a line connecting the master brake cylinder and thehydraulic pressure increasing unit is opened or remains open and thepressure increasing unit is actuated for pressure generation purposes.

In a method of this type with ‘active’ hydraulic brake force boosting,at least part of the brake assistance can be produced actively by meansof the pressure increasing unit. According to the invention, however,the pressure increasing unit in the wheel brakes is actuated for activebrake force boosting already after a braking request or a suspectedbraking request of the driver is detected. Advantageously, it is thuspossible in a case of need to realize a considerably quicker pressurerise in the system and, hence, increase the efficiency of the overallsystem. This is because the pump has already started up whensubsequently the driver depresses the brake pedal further.

Preferably a pump provided in the brake system, in particular ahydraulic pump already provided in brake systems with an anti-locksystem (ABS) or driving dynamics control (ESP system), is used foractive brake force boosting. Therefore, the advantages of the inventioncan be realized without entailing higher expenditure in components.Another advantage lies in the fact that brake force boosting isprincipally freely adjustable by way of a corresponding actuation of thepump and the separating valve.

Any type of pump can be used as a pump that has a sufficiently highcapacity to supply a defined volume of the pressure fluid fast enoughinto the wheel brakes. Preferably, piston pumps are employed. Pistonpumps are less expensive than gear pumps and advantageous in terms ofwear.

When pressure is built up by actuating the pump and with the separatingvalve opened, advantageously, a possibly existing change-over valvebetween the inlet side of the pump and the master brake cylinder isopened to allow the aspiration of pressure fluid through or out of themaster brake cylinder and supply thereof through the pump into the wheelbrakes.

It is provided by the invention that after the actuation of the pressureincreasing unit, a dynamic pressure is produced upstream of theseparating valve and at least clearances in the system are overcome andbrake linings are applied to brake drums or brake discs, respectively.This means that pre-filling of the wheel brakes and application of thebrake linings by means of the pressure generated by the motor isarranged for, with the separating valve open. According to theinvention, the pressure develops due to a dynamic pressure in the systemduring pressure buildup by way of the pump. Due to the brake liningsapplied, the dynamics and more particularly the response behavior of thebrake system of the invention in the low-pressure range is enhanced. Thesystem also offers a high pedal comfort of the brake pedal becausepressure buildup is adjustable in conformity with a desiredcharacteristic curve. Besides, it is additionally possible to generate avery low brake pressure of a few bar, preferably 1 to 2 bar, though, inparticular when a suspected emergency braking situation is detected.

It is arranged for according to the invention that the separating valveremains open at least so long until it is found out that the driver hasinitiated the braking operation.

According to the invention, the initiation of the braking operation bythe driver is detected when the driver touches the brake pedal, appliesa defined force to the brake pedal, and/or it is detected that the brakepedal covers a defined distance from its inactive or initial position inthe actuating direction.

It is arranged for according to the invention that the separating valveremains open for a predetermined time period.

It is arranged for according to the invention that the time period ofthe opening of the separating valve is variably adjusted in accordancewith the brake pedal travel, the brake pedal speed, the brake pedalacceleration, and/or the pressure gradient at the tandem mastercylinder.

It is arranged for according to the invention that the braking requestof the driver is determined on the basis of a movement of the driver'sfoot before the braking operation.

It is provided by the invention that the braking request of the driveris determined on the basis of an accelerator pedal movement such as theaccelerator pedal travel, accelerator pedal return speed, and/oraccelerator pedal return acceleration, before the braking operation.

It is also provided according to the invention that the braking requestof the driver is determined on the basis of the movement of the driver'sfoot when changing from the accelerator pedal to the brake pedal.

It is provided by the invention that the separating valve is a hydraulicvalve, preferably an analogized valve. Corresponding actuation inducessaid valve to also adopt intermediate positions between a (fully) openposition and a (fully) closed position and thus adjust a definedpressure gradient between the two sides of the valve at least inapproximation.

Additional valve functions are further provided. This means that thevalves can be configured as NO-valves open in their non-energizedcondition or NC-valves closed in their non-energized condition. Uponmalfunction of the electric voltage supply of the system or adisturbance of electronic brake control, it is thus possible that thehydraulic connection between the pressure fluid supply reservoir and thepump is closed by an NC-valve and the hydraulic connection between themaster cylinder and the wheel brakes is opened by means of an NO-valve,with the result that braking is reliably ensured at least by means ofthe driver's pedal force boosted by a vacuum brake booster, as the casemay be.

The method is preferably part of a program of an electronic brakecontrol unit for the vehicle brake system.

This object is further achieved by means of a generic brake systemcharacterized in that a detection means is provided in order to detect abraking request of the driver or determine a suspected braking requestof the driver, and in that an electronic evaluating unit for actuatingthe pump and the separating valve is provided which actuates theseparating valve in order to open the connection to the pump andactuates the pump in order to generate hydraulic pressure when thebraking request of the driver is detected or a suspected braking requestof the driver is determined.

It is provided by the invention that the pressure side of the pump isconnected to the wheel brake by way of a hydraulic conduit into which aninlet valve is inserted, the wheel brake of the vehicle is connected tothe master brake cylinder by way of a hydraulic conduit into which anoutlet valve is inserted, and that a pressure sensor is associated withthe master brake cylinder and a wheel speed sensor is associated withthe vehicle wheels.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows a device of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The dual-circuit brake system for motor vehicles shown in the FIGUREcomprises an actuating unit 1, e.g. a tandem master brake cylinder (TMC)with a vacuum brake booster 2 actuated by a brake pedal 3. Arranged onthe actuating unit 1 is a supply reservoir 4 containing a pressure fluidvolume and being connected to the working chamber of the actuating unitin the brake's release position. The one brake circuit illustratedincludes a brake line 5 connected to a working chamber of the actuatingunit 1 and providing a connection between the actuating unit 1 and theone hydraulic unit 22. Brake line 5 includes a separating valve 6forming an open passage for the brake line 5 in the inactive position.Connected in parallel to the separating valve 6 is a non-return valve 7that opens in the direction of the wheel brakes 10, 11 and a pressurelimiting valve 25. Said separating valve is also used herein as apressure modulation unit. The separating valve 6 is usually actuatedelectromagnetically. Preferably, the separating valve is an analogizedvalve. In particular, this design renders possible a continuous ‘analog’adjustment of the pressure or of a pressure reduction, respectively.

The brake line 5 branches into two brake lines 8, 9 respectively leadingto a wheel brake 10, 11. Each of the brake lines 8, 9 contains anelectromagnetically operable inlet valve 12, 19, which is open in itsinactive position and can be switched into a closed position byenergization of the actuating magnet. Connected in parallel to eachinlet valve 12, 19 is a non-return valve 13 opening in the direction ofthe brake cylinder 1. Connected in parallel to these wheel brakecircuits is a so-called return delivery circuit that comprises returnlines 15, 32, 33 with a pump 16. By way of each one outlet valve 14, 17through return lines 32, 33, the wheel brakes 10, 11 are connected tothe return line 15 and, thus, to the suction side of the pump 16 whosepressure side is connected to the brake pressure line 8 in a mouth Ebetween the separating valve 6 and the inlet valves 12, 19.

The pump 16 is preferably designed as a reciprocating piston pump with apressure valve (not shown) and a suction valve. Pump 16 is used hereinas a pressure increasing unit for generating the additional hydraulicbrake force boosting. A low-pressure accumulator 20, comprised of ahousing (not shown) with a spring and a piston, is arranged on thesuction side of pump 16. A non-return valve 34 opening to the pump isinserted into the connection between the low-pressure accumulator 20 andthe pump 16. The suction side of the pump 16 is connected to the brakecylinder 1 by way of a suction line 30 with a low-pressure damper 18 anda change-over valve 31. Further, the brake force transmitting circuitincludes a pressure sensor 40 that is arranged in the brake line 5between the brake cylinder 1 or change-over valve 31 and the separatingvalve 6. The brake cylinder pressure is detected and the introducedbrake pressure determined by way of the pressure sensor 40. The wheelspeeds are determined by the wheel rotational speed sensors 50, 51, andthe signals are sent to an electronic brake control unit 52. Associatedwith the electronic control unit 52 is an evaluating unit 53 foractuating the pump 16 and the separating valve 6 according to a driver'srequest detection unit 54. The detection unit 54 detects a brakingrequest of the driver or a suspected braking request of the driver. Whenthe detection unit 54 detects a braking reauest of the driver or asuspected braking reauest of the driver, the evaluating unit 53 actuatesthe separating valve 6 in order to open the connection to the pump 16and actuates the pump 16 in order to generate hydraulic pressure. In theoreferred embodiment, the detection unit 54 is configured to monitoraccelerator pedal 60 movement and determine the braking request of thedriver or a suspected braking request of the driver on the basis of suchaccelerator pedal 60 movement, for example, the accelerator pedaltravel, accelerator pedal return speed, and/or accelerator pedal returnacceleration before the braking operation.

The brake system operates as follows:

When the driver's request detection unit 54 detects the driver's brakingrequest, then the evaluating unit 53 will actuate the pump 16 and openthe separating valve 6, whereby low pressure is built up that issufficient to overcome the clearances and apply the brake linings of thewheel brake 10, 11. When the driver increases the brake fluid pressurein the system by way of the actuating unit 1 with the vacuum brake forcebooster 2, the pump is actuated for the purpose of additional pressureincrease in the wheel brakes by means of the electronic control unit 52,as the case may be, only when a point of maximum boosting of the vacuumbrake booster 2 is reached or exceeded. Thus, the pump fulfils thefunction of an additional, active hydraulic brake force boosting. Whenthe brake pressure introduced into the system and the wheel brakesreaches or exceeds a value and when the wheels are transferred intobrake slip, then ABS control will be initiated by the electronic controlunit 52 in response to the signals of the wheel speed sensors 50, 51,and the inlet and outlet valves 12, 14, 17, 19 are actuatedcorrespondingly.

1. A method of controlling a hydraulic vehicle brake system with active hydraulic brake force boosting, wherein brake pressure is introduced into a master brake cylinder by means of an actuating device and the introduced pressure is boosted by means of an active hydraulic pressure increasing unit, comprising: monitoring movement of an accelerator pedal; detecting a braking request or a suspected braking request based on accelerator pedal movement, opening or maintaining open a separating valve arranged in a line interconnecting the master brake cylinder and the hydraulic pressure increasing unit and actuating the pressure increasing unit in response to the detection of a braking request or a suspected braking request; monitoring a brake pedal to detect initiation of a braking operation; and maintaining the separating valve open until it is detected that a braking operation has been initiated.
 2. Method as claimed in claim 1, wherein a braking request or a suspected braking request is detected based on accelerator pedal travel, accelerator pedal return speed, or accelerator pedal return acceleration before the braking operation.
 3. Method as claimed in claim 1, wherein after the actuation of the pressure increasing unit, dynamic pressure is produced upstream of the separating valve and at least clearances in the system are overcome and brake linings are applied to brake drums or brake discs, respectively.
 4. Method as claimed in claim 1, wherein initiation of a braking operation is detected when the brake pedal is moved in the actuating direction a defined distance from an initial position or a defined force is applied to the brake pedal.
 5. Method as claimed in claim 1, wherein the separating valve remains open for a predetermined time period after it is detected that a braking operation has been initiated.
 6. Method as claimed in claim 1, wherein the separating valve is a hydraulic valve.
 7. Method of controlling a hydraulic vehicle brake system with active hydraulic brake force boosting, wherein brake pressure is introduced into a master brake cylinder by means of an actuating device and the introduced pressure is boosted by means of an active hydraulic pressure increasing unit, comprising: monitoring movement of an accelerator pedal; detecting a braking request or a suspected braking request based on accelerator pedal movement, opening or maintaining open a separating valve arranged in a line interconnecting the master brake cylinder and the hydraulic pressure increasing unit and actuating the pressure increasing unit in response to the detection of a braking request or a suspected braking request; monitoring a brake pedal, and wherein a duration in which the separating valve is maintained opened is variably adjusted in accordance with a detected brake pedal travel, a detected brake pedal speed, a detected brake pedal acceleration, or a pressure gradient at the master cylinder.
 8. A hydraulic brake system for vehicles comprising: a master brake cylinder operable by means of an actuating device; at least one pump whose pressure can be applied to at least one wheel brake of the vehicle for the purpose of generation of hydraulic brake force boosting, the pump is connected to the master brake cylinder by way of a first hydraulic conduit; a separating valve positioned along the first hydraulic conduit; a detection unit configured to detect a braking request or a suspected braking request; and an evaluating unit configured to actuate the separating valve to an open position and actuate the pump to generate hydraulic pressure in response to the detection of a braking request or a suspected braking request and to further maintain the separating valve open until it is detected that a braking operation has been initiated.
 9. The hydraulic brake system of claim 8, wherein the detection unit detects a braking request or a suspected braking request based on movement of an accelerator pedal.
 10. The hydraulic brake system of claim 9, wherein the detection unit detects a braking request or a suspected braking request based on travel of the accelerator pedal, accelerator pedal return speed, or accelerator pedal return acceleration before the braking operation. 